THE SUPREME COURT recently gave truckers a green light to destroy the interstate highway system. With a February 21 ruling that rebuffed Connecticut's bid to keep double-trailer trucks off its highways, the high court decided it will sit by to watch a 42.500-mile highway system crumble further.

Originally, the 1983 Surface Transportation Act struck down laws in Massachusetts, Connecticut and 11 other states that outlawed the juggernauts, which consist of two 28-foot trailers linked together to make a rig 15 feet longer than the longest single trailers moved to ban the from its roads altogether, Massachusetts's laws restricted 60-feeters to the Turnpike.

Tests by the Department of Transportation (DOT) have shown conclusively that five-axeled trailer rigs carrying 99,000 pounds of cargo--the ostensible limit--do as much damage to a highway as 96 cars. Moreover, DOT spot checks have also found that at any time 25 to 35 percent of all trucks on the road to as much as 133,000 pounds every additional 1000 pounds cargo does more than just 1000 pounds' worth of damage.

When the government began constructing the interstates in the 1950s, truck weight limits were about two-thirds of what they are now. Projected traffic volume has everywhere outstripped what the government expected, largely because it was a self-perpetuating cycle--when truckers saw a fabulous new system of highways come in, they moved quickly to take business from the railroads, and as the government saw demand for the highways grow, both from truckers and a postwar America that was buying more and more automobiles, it planned longer and larger interstates, further encouraging truckers to grow.

The interstates were built with the expectation that they would need to be overhauled in 20 years, says Lawrence A. Staron of the Federal Highway Administration. But he adds, "if traffic volumes are very different from what we expected, what we designed for 20 years might last only 10."

Just keeping up with the deterioration of the highways will cost $2.4 billion in 1985, according to Staton, but a 1980 study showed that a least 30,000 miles of the system would have to be rehabilitated during this decade. Rehabilitation, of course, can mean anything from simple resurfacing to wholesale rebuilding--where resurfacing runs about $500,000 per mile and rebuilding anywhere from $5 million a mile in uncluttered rural areas to an "unlimited sum" for urban environs, Staron says.

There is little sense in double rigs with theoretical weight equal to those of 45-foot trailers, but with 11 tempting feet of extra cargo space. These trucks provide a ripe opportunity for the unscrupulous trucker--and more than one-quarter of them are unscrupulous--to overload in pursuit of bigger profits. The Motor Carrier Act of 1980 deregulated the industry, finally making it a competitive one--and 3000 new carriers seized the opportunity to grab permission to run on 36,000 new routes in 1983. The competition is brutal; the railroads have moved in to grab back a full 10 percent of the transportation market, and about 300,000 truck-driving Teamsters have lost jobs since 1979. Operators have slashed rates feverishly and often foolishly to attract business. And no doubt they are illegally overloading their rigs to recoup their losses.

KEEPING THE double-rigs off the highway will not spell the demise of the trucking industry. In the short-haul and rapid-shipment markets, trucks will always prove more efficient than railroads, and that market will never be threatened.

It is important to remember that trucks only entered the intercity long-haul market in the first place because the government dished up the interstate highway system, and regulations for a long time made that market artificially attractive to them. Permitting double rigs is just another way of encouraging trucks to serve a market--long-haul transportation--in which railroads are up to four times as fuel efficient and less expensive, and where truckers are not really maximizing their profits.

Connecticut had the right idea. Its Attorney General, Joseph Lieberman, made as his major case against the double-trailers the fact that they roll and sway uncontrollably on what in his state are commuter-laden highways--which is true. But the less dramatic and still more serious case against the double-monsters lies in the damage that they and their single-trailer brothers do to the highways--damage brought home forcefully in Connecticut last year when a crumbling bridge on Interstate 95 fell in and took a woman's life with it.